The present invention relates generally to a process for measuring electric voltages and/or electric field intensities and more specifically to a sensor for carrying out this measuring process.
Known processes and correspondingly used sensors of this type are based on the principle of the linear electro-optical effect of various crystals.
Measuring processes and sensors for such processes are known which are based on the principle that the refractive index of certain crystals, which are transparent for light waves, can be changed as a function of an electric field intensity generated in the crystal. Crystals made of lithium niobate or potassium dihydrophosphate, for example, have this so-called electro-optical effect. Two electrodes are arranged on a surface of a crystal wafer in parallel and at a distance from one another, for example, for measuring an applied voltage, by the resulting change of the refractive index which is a function of the applied voltage.
For determining the refractive indices, interferometric arrangements or polarimetric arrangements are known. In the interferometric arrangement or process, the phase of a light wave is modulated and superimposed on a reference wave which leads to an intensity change of the coupled-out light wave. In the case of the polarimetric arrangement or process, the polarization of a polarized light wave is changed as a function of the refractive index and the intensity change is determined by a polarizer.
Both known arrangements require relative high technical expenditures. In addition, the materials to be used cause implementation problems. In addition to occurrence and the requirement of high electro-optical effects of the materials, there occurs in these materials, piezo-electric as well as elasto-optical effect which together have the same appearance as the purely electro-optical effect. The inertia of the material will then have the result that, in the area of low frequencies, the electro-optical effect, on the one hand, and the piezo-electric effect and elasto-optical effect, on the other hand, are superimposed on one another. The transition range is also characterized by resonance phenomena which result from crystal oscillations.
Therefore, for a broad-band measuring system, the exclusive utilization of the purely electro-optical effect is required; that is, the corresponding piezo-electric/elasto-optical effects must be negligible.
In the case of the polarimetric arrangement, this situation must be met simultaneously for two coefficients, while, in the case of an interferometric arrangement, one coefficient will be sufficient. Therefore, a much larger number of materials are available for the construction of a broad-band interferometric measuring system than for a broad-band polarimetric measuring system. However, a disadvantage are the considerable technological expenditures of an interferometer. In addition, integrated-optical components must be used for this purpose, to which optical power must be fed by a defined mode and by a defined polarization. During the use of this technology in practice, the use of a polarization-maintaining optical wave guide (HiBi-fiber) is therefore absolutely necessary.
An object of the present invention is to provide a process and a sensor for implementing this process by which the advantages of the interferometric process can basically be maintained, specifically the necessity of the evaluation of only a single electro-optical coefficient. In addition, the technical expenditures are to be minimized by the fact that neither an integrated-optical technology is to be used, nor must a special optical wave guide be applied.
The invention is particularly distinguished by the fact that the light wave must only be sent through the crystal, and must therefore be coupled in and coupled out. The deflection of the light wave to be coupled out or of the coupled-out light wave can be determined and evaluated by simple devices.
Further advantageous details of the invention are found in the subclaims and will be explained in detail in the following by means of the embodiment illustrated in the drawing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.